An image sensor is a device which receives light from an optical image or one or more objects and converts the received light into electrical signals forming an image. Recently, with the development of applications that use or are based on imaging from image sensors including the computer industry and communication industry, the demand for an image sensor having improved performance is increasing in various fields or applications, including, e.g., a digital camera, a camcorder, a portable device such as a personal communication system including a smart phone, a wearable device, a game machine, a security camera, a medical micro-camera and a robot.